1. Field of the Invention
The present invention generally relates to a sensor for sensing concentrations of a solute in a solution and, in particular to method and apparatus for sensing concentrations of a solute in a solution such as a liquid ink or a liquid developer for use in a liquid developing electrostatic recording apparatus.
2. Description of the Related Art
There has been proposed a solute concentration detecting apparatus allowing automation of concentration adjustment in Japanese Patent Unexamined Publication No. 7-55682. More specifically, a solution reservoir is provided with a vertical passage through which two floats having different specific gravities are moving in a solution depending on the concentration of the solution. In the case of reduced concentration, one float having a smaller specific gravity is floating and the other having a greater specific gravity is sinking down As the concentration of the solute becomes higher, the other float having the greater specific gravity is floating and finally comes in contact with the one float having the smaller specific gravity. Therefore, when detecting the contact, it is determined that the concentration of the solution has reached the target concentration.
However, the above-mentioned concentration detecting apparatus can determine only whether the concentration of the solution has reached the target concentration. On other words, according to the conventional arrangement, only discrete concentration values are obtained. Therefore, precise concentration adjustment cannot be achieved.
Further, since the two floats are moving through the vertical passage, it is necessary to provide space for the vertical passage in the solution reservoir, resulting in increased size of the solution reservoir and reduced flexibility in design.